1. Field of the Invention
This invention relates to an optical head associated with plural optical recording mediums of different types and to an optical disc device for recording and/or reproducing signals for plural optical discs of different types using such optical head.
2. Description of Related Art
As an optical recording medium, a replay-only optical disc, called a CD (Compact Disc), or a write-once optical disc, called CD-R (Compact Disc-Recordable), is being put to practical use. These optical discs are in widespread use because the discs are superior in mass-productivity and can be manufactured at low cost, while being usable for recording or reproducing the information in high stability.
Meanwhile, in these optical discs, the recent tendency is towards higher recording capacity. Amidst this tendency, the DVD (Digital Versatile Disc/Digital Video Disc) which, despite the fact that its outer diameter is equal to that of the CD, has a drastically improved recording capacity, such that data corresponding to a motion picture can be stored therein with the picture quality comparable to that of the current television broadcast, has been developed and put to practical use. In this DVD, the laser light shorter in wavelength than the laser used for a CD is used for recording and/or reproducing the information in order to elevate the recording density to increase the recording capacity.
As to an optical disc device, employing a so-called compatible optical disc as a recording medium such an optical disc device has been developed in which there is provided an optical head capable of recording and/or reproducing not only the information for the DVD but also that for the CD or CD-R.
Meanwhile, in the optical head capable of accommodating both the CD or the CD-R and the DVD, the optical system for the CD or the CD-R desirably has as many portions in common with the optical system for the DVD as possible, in order to reduce the overall size of the head or to lower the manufacturing cost.
In order to meet this demand, development of an optical head having a so-called double-wavelength semiconductor laser for selectively radiating the laser light for coping with the CD or the CD-R and the laser light for coping with the DVD, is underway.
In the double-wavelength semiconductor laser, a light source for radiating the laser light adapted for coping with the CD or the CD-R and a light source for radiating the laser light adapted for coping with the DVD are arranged in proximity to each other and are housed in the same package. This optical head also is provided with a light receiving element for receiving the return beams of the laser light beams reflected back form the optical disc in order to enable detection of tracking error signals or focussing error signals adapted for coping with the CD or the CD-R and with the DVD. This light receiving element has plural light receiving sections which are obtained on splitting the element to permit the return light beams of the laser light beams reflected back from the optical disc to be illuminated on pre-set portions of the optical disc.
However, in this optical head provided with the double-wavelength semiconductor laser, there are occasions wherein, if the distance between the light sources is deviated from a pre-set design value, the return beams of the laser light beams radiated from these light sources cannot be properly received by the plural light receiving sections of the light receiving element.
Thus, this optical head cannot detect the focussing error signals or the tracking error signals adapted for coping with both the CD or the CD-R and the DVD, such that, when the optical head is loaded on an optical disc device, the focussing control for focussing the objective lens on the signal recording surface of the objective lens or the tracking control for permitting the laser light spot to follow the recording track on the signal recording surface of the optical disc cannot be performed properly.
It is therefore an object of the present invention to provide an optical head in which return light beams of respective laser light beams radiated from the light sources of light radiating means, which are housed in the same package and which radiate laser light beams adapted to cope with plural optical recording mediums of different kinds, can be properly received by plural light receiving sections of the light receiving means. It is another object of the present invention to provide an optical disc device which enables signals to be recorded and/or reproduced to or from plural optical recording mediums of different kinds.
In one aspect, the present invention provides an optical head adapted for coping with a plurality of optical recording mediums of different types, in which the optical head includes light radiating means having a first light source for radiating the first laser light and a second light source for radiating the second laser light with a wavelength different from that of the first laser light, light converging means for converging the laser light from the light radiating means towards the optical recording medium, a beam splitter for separating the optical path of the laser light proceeding towards the optical recording medium and that of the laser light reflected from the optical recording medium and light receiving means for receiving the return laser light reflected back from the optical recording medium. The first and second light sources are housed in the same package. The relative positions of the first and second light sources of the light radiating means are so set that a straight line interconnecting a spot position of the first laser light illuminated on the optical recording medium and a spot position of the second laser light illuminated on the optical recording medium will be substantially perpendicular to a recording track of the optical recording medium. The light receiving means includes a plurality of light receiving sections obtained on splitting by a splitting line substantially parallel to a straight line projected on the light receiving means, the straight line being such a line interconnecting a spot position of the first laser light illuminated on the optical recording medium and a spot position of the second laser light illuminated on the optical recording medium.
In another aspect, the present invention provides an optical head adapted for coping with a plurality of optical discs of different types, in which the optical head included a semiconductor laser having a first light source for radiating the first laser light and a second light source for radiating the second laser light with a wavelength different from that of the first laser light, an objective lens for converging the laser light from the semiconductor laser on the optical disc, a beam splitter for separating the optical path of the laser light proceeding towards the optical disc and that of the laser light reflected from the optical disc from each other and a light receiving element for receiving the return laser light reflected back from the optical disc. The first and second light sources are housed in the same package in proximity to each other, with the semiconductor laser selectively emitting the first laser light or the second laser light depending on the disc type. The relative positions of the first and second light sources of the semiconductor laser are so set that a straight line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light illuminated on the optical disc will be substantially perpendicular to a recording track of the optical disc. The light receiving element includes a plurality of light receiving sections obtained on splitting by a splitting line substantially parallel to a straight line projected on the light receiving unit, the straight line being such a line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light similarly illuminated on the optical disc.
In yet another aspect, the present invention provides an optical disc device for recording and/or reproducing signals in association with a plurality of optical discs of different types, in which the apparatus includes a spindle motor for rotationally driving the optical disc, an optical head adapted for coping with the plural optical discs of different types and a signal processing circuit for generating playback signals and control signals based on signals detected by the optical head. The optical head includes light radiating means having a first light source for radiating the first laser light and a second light source for radiating the second laser light with a wavelength different from that of the first laser light, an objective lens for converging the laser light from the light radiating means towards an optical disc, a beam splitter for separating the optical path of the laser light radiated from the light radiating means into an optical path of the laser light proceeding towards the optical disc and that of the laser light reflected from the optical disc and a light receiving element for receiving the return laser light reflected back from the optical disc. The first and second light sources are housed in the same package. The relative positions of the first and second light sources of the light radiating means are so set that a straight line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light illuminated on the optical disc will be substantially perpendicular to a recording track of the optical disc. The light receiving element includes a plurality of light receiving sections obtained on splitting by a splitting line substantially parallel to a straight line projected on the light receiving means, the straight line being such a line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light similarly illuminated on the optical disc.
According to the present invention, as described above, the return light from an optical recording medium illuminated by the first light source and the return light from the optical recording medium illuminated by the second light source can be properly illuminated on split portions of plural light receiving sections obtained on splitting along a splitting line subsequently, which is parallel to a straight line interconnecting the spot position of the first laser light illuminated on the optical recording medium and the spot position of the second laser light, and which is projected on the light receiving sections, even if an error is produced between the first and second light source of the light radiating means.
Therefore, with the optical head embodying the present invention, the light reception signals for generating the focussing error signals or the tracking error signals, adapted for coping with plural optical recording medium of different types, such as CD-R or DVD., can be detected appropriately.
Moreover, with the optical disc device embodying the present invention, provided with the above-described optical disc device, it is possible to record and/or reproduce signals for plural optical discs of different types.